Differential pressure transmitters have long been known in the art. Typical differential transmitter systems are illustrated in, for example, my prior U.S. Pat. No. 5,117,867, the disclosure of which is incorporated herein by reference.
As explained in my prior patent, a differential pressure transmitter system is used with a pipeline in which there is a flowing media which needs to be measured as to flow rate. An accurate and economical method of measuring flow rate is to install an orifice in the pipeline. The orifice causes a differential pressure as media is forced through the small opening of the orifice, which is differentially sensed by a transmitter through process pressure signal lines. The amount of differential pressure developed is a square root function of the flow rate. Consequently, by knowing the size of the precision opening in the orifice plate, and by obtaining a precision measurement of the differential pressure, the flow rate may be calculated with greater than one percent accuracy.
It is conventional to provide a valve manifold to interface with the two process pressure signal lines from the orifice. However, all manifolds providing complete functionality have required at least three and, in some cases, five separate valve handles. The multiplicity of handles, and the precise sequence required to obtain the desired functions, has led to an overly complicated system that requires careful training and consistent execution to obtain accurate results and avoid damaging the equipment. The differential pressure transmitter is a relatively delicate instrument, and a high degree of care and consistent operation by workers in the field is required to avoid damage.